chip in some comments from me
Standard form 172 is gonna be faster anyday. A 150Tdi is about the same as a petrol Gti probably coz of the rev limiter n so forth. It will feel heaps quicker htan the petrol GTi coz of the torque.
I think tunability. Turbo of coz have hte advantage but petrol turbo can be played around to. 285 on 1.8T with some kit from Germany or USA.
Golf doesnt offer hack alot of standards compare to172 (in NZ anyway) Golf seems to hold up their resales quite well here i dont know if that applies to u guys.
If u r lookin to do some track or very sporty driving. NO GOLF (I own a golf 4 too) 172 all the way. Build wise Golf is much better.
If u want refinement, comfort, build quality, ECONOMY (diesel doesnt drink much) then GOLF go for it , its still a very good car. (suspension on Golf even with factory sport kit (non standard) its still soft compare to stadnard 172 suspension) Golf suspension tends to loose itself when the road get uncertain,... kind of like runnin out of sequence
172 not so refine, not as big, not as well built but quicker in standard form, its good handling car for a Front wheel drive. Its more FUN
.
Diesel is also much louder especially those 1.9L Tdi engines they seem to bring out that diesel sound very well. (bad if u dont like it haha)
hope that help
if u really want a sporty golf .. then u are payin as much as a Clio V6 in the R32 Golf form